04. A Superconductivity Jam-Up
James Séamus Davis
James C. Séamus Davis, Physics, and his research team explained why superconductivity can be stalled by a form of electronic gridlock. The researchers found that copper oxides, or cuprates, can serve as high-temperature superconductors, but in a slightly different configuration, they become stalled. Understanding how and why that transition takes place is a crucial question for cuprate superconductivity research, since if the gridlock did not occur, the maximum temperatures for superconductivity could be much higher. Scanning lightly hole-doped cuprate crystals with a highly precise scanning tunneling microscope (STM) revealed strong variations in electronic structure with some copper-oxygen-copper (Cu-O-Cu) bonds distributed randomly through the crystal exhibiting “holes” where electrons are missing. The researchers also found larger rectangular regions with missing electrons that were spaced four units of the crystal lattice apart, which may represent the first direct observation of long-sought electronic stripes in cuprates. This new research’s innovation was to compare current flow in opposite directions at each point in the scan in a process called tunneling asymmetry (TA) imaging. At regions of the crystal containing fewer electrons (more holes), more electrons can flow down into these voids than up. TA imaging might also reveal if the electronic stripes are made up of the same kind of holes and precisely how the hole patterns suppress superconductivity.